1. Field of the Invention
This invention relates to an ultrasonic coupler and a method for the production thereof More particularly, it relates to an ultrasonic coupler to be interposed between an ultrasonic probe used in the field of bioinstrumentation utilizing an ultrasonic wave and the surface of contact of a probe with an analyte under test and to a method for the production thereof.
2. Description of the Prior Art
The ultrasonic diagnostic apparatus, owing to the simplicity of handling and the obviation of the necessity for penetrating a patient's body, has found utility in numerous fields of diagnosis represented by those directed to the abdominal organs such as the heart and the liver.
In the case of a patient of cardiac disorder, to ensure precise performance of cardiotomy, the location and shape of a lesin, the relation of the lesion to normal parts adjoining it, and so on are preferable to be diagnozed in detail in advance of the operation. Particularly in the case of a neonate suffering from a serious cardiac disorder, this detailed diagnosis constitutes an important matter deciding between success and failure of the outcome of the surgical operation. The accurate preoperative diagnosis realized by the use of the ultrasonic diagnostic apparatus has been contributing conspicuously to improving the results of such surgical operations in recent years. By the preoperative sonic examination performed with a probe applied to the walls of the chest covering the heart but avoiding the lungs and the osseous tissues, no sufficient information can be obtained about cardiac diseases and lesions. As a way of making an ultrasonic diagnosis in detail beyond the limits of the sonic examination, the ultrasonic examination to be performed during the course of a cardiotomy may be conceived. When the ultrasonic examination is performed after a mediad incision of the sternum by directly applying a probe externally on the pericardium, the heart, or the blood vessel prior to the incision thereof affords the surgeon a detailed surgically useful diagnosis concerning the pertinent internal cavity. Further, the diagnosis enables the surgeon, in the course of operation, to confirm whether or not the surgical treatment initiated in consequence of the ultrasonic examination is adequate. This fact is important for preventing repetition of surgical operations and conducting postoperative management of the operated organ.
In the ultrasonic diagnosis, a cross-sectional image of a living body is obtained by a process which comprises projecting an ultrasonic pulse toward the interior of the body from the surface of the body or the surface of a relevant organ and receiving a reflected wave to be produced by the difference between acoustic impedances proper to varying tissues within the living body. For the purpose of obtaining an exact cross-sectional image, therefore, it is necessary that the ultrasonic probe should be applied to the surface of a body or the surface of a relevant organ tightly enough to preclude intervention of an air layer which exhibits a high reflectance to the ultrasonic wave.
When the probe is applied directly to the surface of a body as described above, however, the blood vessels and other tissues near the body surface are reproduced in the image in a shape deformed by pressure. When the ultrasonic examination is carried out by directly applying the probe to the heart or the wall of a blood vessel, the image is liable to register signs of arrhythmia and lowered blood pressure because the heart and the blood vessel are producing ununiform motions with an accompaniment of heartbeats and further because the probe exerts pressure on the surface of contact. It is, therefore, difficult to ensure safe use of the probe of the conventional type provided with a contact surface incapable of deformation by keeping this probe incessantly in tight contact with the surface of the heart or some other similar pulsating organ. In the existing true state of affairs, the usefulness of the real-time ultrasonic cross-section examination method to be performed during the course of a surgical operation is not manifested fully satisfactorily.
This situation is in need of a proper contact medium to be used between the probe and the surface of the body or the surface of a relevant organ, namely an ultrasonic coupler which possesses suppleness enough to follow the motion of the surface of the heat, for example, while remaining in tight contact therewith and excels in ultrasonic properties.
In the conventional ultrasonic coupler of this kind, a projected part 1a of the portion of an elastic acoustic medium 1 which is destined to contact a subject 2 under test is projected from an opening 4 on the subject side of an immobilizing member 3 in the same width as the width W of the opening, namely in the identical area with the area of the opening as illustrated in FIG. 1A and FIG. 1B (JP-A-61-288,840(1986)). The surface of the elastic acoustic medium 1 which contacts an ultrasonic wave-receiving surface 5a of an ultrasonic probe 5 has a flat shape. Further, no unified method has been established as to attaching means and positioning means employed for the attachment of an ultrasonic coupler to the ultrasonic probe 5. No unified method has yet been established as to means for stowing the elastic medium 1 in the immobilizing member 3.
With respect to the shape of the ultrasonic coupler, an ultrasonic coupler so shaped that the cross section of the elastic acoustic medium 1 taken perpendicularly to the direction of ultrasonic scanning decreases in width in the direction of transmission of ultrasonic wave as illustrated in FIG. 2A, FIG. 2B and FIG. 2C (JP-A-63-36,173(1988)) and an ultrasonic coupler so shaped that the cross section of the elastic acoustic medium 1 taken parallelly to the direction of ultrasonic scanning and also to the direction of ultrasonic wave transmission has a rectangular shape or has a width increasing in the direction of the ultrasonic wave transmission (JP-A-63-117,7345(1988)). The conventional ultrasonic couplers of this kind invariably have an elastic acoustic medium 1 projected toward the subject side from the immobilizing member.
Where the elastic acoustic medium projects from the subject side opening of the immobilizing member in the same width as the width of the opening as found in the conventional ultrasonic couplers, however, a movement of the ultrasonic coupler on the subject 2 results in impairment of a produced image because the elastic acoustic medium 1 is inevitably flexed and the desired transmission and reception of an ultrasonic wave is consequently obstructed as illustrated in FIG. 1B. Otherwise, the flexure of the elastic acoustic medium 1 poses a problem that the elastic acoustic medium eventually sustains breakage. Further, since the surface of the elastic acoustic medium 1 destined to contact the surface of the ultrasonic probe 5 for transmitting and receiving an ultrasonic wave is flat, bubbles (air) are suffered to enter the surface of contact which is formed between the elastic acoustic medium and the surface of the ultrasonic probe for transmitting and receiving an ultrasonic wave during the attachment of the ultrasonic coupler to the ultrasonic probe. The entrapped bubbles pose a problem that the transmission of an ultrasonic wave to the subject is not carried out favorably.
Again with respect to the shape of the ultrasonic coupler, since the cross section taken parallelly to the direction of ultrasonic scanning and also to the direction of transmission of an ultrasonic wave assumes a fixed rectangular shape or increases in width in the direction of transmission of an ultrasonic wave, the size of the ultrasonic coupler is limited to the visible dimensions of the ultrasonic probe and, as a result, the shape of the ultrasonic coupler is larger than the area in which the ultrasonic beam is transmitted and received. This fact constitutes itself a factor for degrading the contacting property of the ultrasonic coupler with the subject or the scanning property of the ultrasonic coupler on the subject.
An object of this invention, therefore, is to provide a novel ultrasonic coupler.
Another object of this invention is to provide an ultrasonic coupler which precludes the impairment of a produced image due to the retaining property of the elastic accoustic medium and the flexure of the elastic acoustic medium acoustic medium and the entrapment of bubbles during the attachment of the ultrasonic coupler to the ultrasonic probe and, which is more, improves the contacting property with the subject and the operability.
A further object of this invention is to provide an ultrasonic coupler which allows simple manufacture and easy handling and has been sterilized and a method for the production thereof.